Conventionally, an engine rotation speed control device is known which has a control means reducing a target engine rotation, speed for the safety. For example, the Patent Literature 1 discloses a rotation control device of a diesel engine for a ship which reduces a fuel injection amount so as to reduce a target engine rotation speed in the case that a command engine rotation speed by a control lever in abnormality detection mode is equal to or more than a predetermined value and an actual engine rotation speed is equal to or more than the predetermined value.
In the rotation control device of the diesel engine for the ship disclosed in, the Patent Literature 1, an object to be controlled, is the engine rotation speed. Therefore, in the case that the reduction tendency of the ship speed itself is not necessarily in agreement with that of the engine rotation speed, an operator cannot feel softly the deceleration at the time of detecting the abnormality of the engine. In other words, in an engine rotation speed control device having a control means for reducing the target engine rotation speed for the safety, in the case that reduction tendency of an output speed of an object driven by the engine is not in agreement with that of the engine rotation speed, an operator cannot feel softly the deceleration at the time of detecting the abnormality of the engine.
Patent Literature 1: the Japanese Patent No. 2689119